The subject matter disclosed herein relates to hand dryers, and in particular, to a hand dryer that automatically adapts to different input voltages.
Universal brushed AC blower vacuum motors are commonly used in hand dryers because their widespread use in other applications, such as floor care equipment, provides availability and lower costs due to economies of scale. High speed or fast drying hand dryers will typically use universal brushed AC blower vacuum motors due to the desirable pressure and flow characteristics of these blowers and their effectiveness in drying hands with shortened dry times. Universal brushed AC blower vacuum motors used in hand dryers range in size from 500-1200 watts input power.
High speed or fast drying hand dryers will typically include a heating element for user comfort that heats air during a drying cycle. Heating elements for hand dryers are typically produced as nichrome wire coils or ribbon wound around a heat-resistant support form. The heating elements are a purely resistive electrical load and typically are typically sized between 400-1900 watts for a hand dryer.
Typical electric circuitry in hand dryer controls will separate the control circuits for a blower vacuum motor and heating element into individual parallel control circuits. In this manner, the control of the blower vacuum motor is not dependent on the operation of the heating element. If the heating element were to fail and cease function, its operation or lack of operation does not impact the function or operation of the blower vacuum motor.
Hand dryer customers desire long, uninterrupted service life with low maintenance, so extended motor brush service life is a desired feature especially in washrooms with high user traffic. Hand dryer customers desire more energy efficient hand dryers as they become more aware of the need for energy conservation and the capacity and efficient management of electrical utility distribution networks.
Universal voltage controllers are becoming a more popular feature of hand dryers since they provide customers the flexibility of installing a single hand dryer model over a range of supply voltages from 120-277 VAC. Typical nominal supply voltages would be 120, 208, 240 or 277 VAC. The universal voltage controllers used in current state of the art hand dryers that incorporate brushed AC blower vacuum motors typically use a technique involving a semiconductor switching device, such as a triac, to manipulate the input voltage supply waveform to regulate the input voltage to the motor and/or heating element, thereby permitting the operation of the hand dryer over a range of input supply voltages from 120-277 VAC. The universal voltage controller includes a means for detecting the input voltage while software in the universal voltage controller defines how the waveform is manipulated depending on the specific ranges of input voltage. A typical hand dryer incorporating a universal brushed AC blower vacuum motor, heating element, and universal voltage controller may have a motor designed and manufactured to operate at a single optimum motor input voltage such as 120 VAC. When supplied with a voltage other than the motor's designed input voltage, the universal controller's embedded software controls the semiconductor switching device to manipulate the waveform of the input voltage to adjust the nominal voltage supplied to the motor and/or heating element. In this case, the input power supply's waveform is changed from the normally expected AC sine waveform to an alternative waveform resulting in the nominal voltage of the waveform being adjusted to a voltage compatible with the motor's design. While this is a common approach used for universal voltage controllers for hand dryers, there are inherent drawbacks.
With the typical approach to universal voltage control used in hand dryers described above, the manipulated waveform can be significantly changed from a normally expected AC sine wave. The resulting changes in the current waveform supplied to the universal brushed AC blower vacuum motor can significantly affect the operating characteristics of the motor's carbon brushes and result in a brush life reduction of 25-50% or greater, as compared with using the normally expected AC sine wave. The resulting shortened motor brush life conflicts with the customer's desire for long, uninterrupted service life.
Another drawback of the described traditional method of universal voltage control for hand dryers is the negative impact on the hand dryer's operational power factor when the normally expected AC sine wave is manipulated to adjust the voltage to the motor. Power factor is a measure of how efficiently electrical power is consumed and is defined as the ratio of real power to apparent power. A purely resistive electrical load is 100% efficient in consuming electrical power and has a power factor of 1. An electrical load that is a combination of resistive and inductive load is less efficient in consuming electrical power and has a power factor less than 1. The lower the power factor of an electrical load, the less efficient it is in consuming electrical power. Power factors less than 1 impact total power consumption, power availability from the power supply, electrical losses in transformer and distribution equipment, and electricity bills. In some examples of hand dryers incorporating universal voltage controllers using the typical approach described above, the power factor of the hand dryer can be reduced to a power factor 0.6 or lower when operating at supply voltages that are different than the design voltage of the motor.
Another drawback of the described traditional method of universal voltage control for hand dryers is sensitivity of the control function to the frequency of the input power supply. In the traditional method for universal voltage control, the software defines how the input waveform is manipulated in response to a specific input voltage and is typically dependent on the frequency of the power supply. The traditional method of manipulating the waveform is dependent on the duration of a half cycle of the alternating waveform. A 60 Hz power supply has a half cycle duration of 8.3 milliseconds (ms), while a 50 Hz power supply has a half cycle duration of 10.0 ms. A traditional universal voltage control for hand dryers designed for 60 Hz operation will develop different motor input voltage and operating characteristics when supplied with a 50 Hz power supply. Multiple control systems typically are developed to address different power supply frequencies.